| 摘要 |
PURPOSE:To considerably improve the toughness in the direction at a right angle to the rolling direction by adding Ca to the high-strength bar steel material of medium carbon and medium sulfur level and applying heat treatment such as hardening and tempering. CONSTITUTION:The billet or cast billet of the medium carbon steel containing C; 0.30-0.50%, Mn; 0.40-1.80%, Si; 0.10-0.40%, S; 0.010-0.030%, Cr; 0.50- 1.20%, Mo; 0.10-0.50%, Sol, Al; 0.015-0.060%, Ca; 0.0010-0.0100% is hot- rolled to bar form at rolling ratio 8 or more. The existence of Ca reduces MnS inclusions, prevents the stretching of MnS through rolling, granulates the same and improves the toughness of the C direction at a right angle to the rolling direction. Next, the bar material is hardened from 20-60 deg.C above its Ac3 point and is then tempered at 400-650 deg.C, whereby its toughness and tensile strength are further improved. |
